Solubility and Diffusivity of Hydrofluoroolefin Refrigerants in a Polyol Ester Lubricant

Abstract

To support the phaseout of high global warming potential working fluids commonly used in air-conditioning and refrigeration systems, detailed knowledge about the thermodynamic and transport properties of replacements, for example, hydrofluoroolefins (HFOs), in lubricant oils is required. In this context, isothermal experimental vapor–liquid equilibrium (PTx) and diffusivity measurements for 2,3,3,3-tetrafluoropropene (R-1234yf) and trans-1,3,3,3-tetrafluoropropene (R-1234ze (E)) in a synthetic polyol ester lubricant (ISO VG 32) were performed using a gravimetric microbalance over a temperature range from 248.15 to 348.15 K and pressures of up to 0.6 MPa. A nonrandom two liquid (NRTL) activity coefficient model was applied to correlate the measured solubility for each HFO/lubricant mixture. The diffusivities of R-1234yf and R-1234ze (E) in ISO VG 32 oil were determined from time-dependent absorption data based on a one-dimensional diffusion equation. The calculated diffusivities ranged from 10–12 to 10–10 m2·s–1 and were dependent on temperature and refrigerant composition.

Viscosity and Density of a Polyol Ester Lubricating Oil Saturated with Compressed Hydrofluoroolefin Refrigerants

“…The density, viscosity, and the respective uncertainty data for pure ISO VG 32 lubricating at ambient pressure as a function of temperature from 248.15 to 348.15 K were previously reported by our group and are depicted in Table .…”

“…In the present study, the excess dynamic viscosities and excess volumes of liquid HFO/ISO VG 32 lubricating oil mixtures were correlated. Solubility correlations for those HFO/ISO VG 32 lubricating oil systems using an NRTL activity coefficient model were previously reported by our group . In the modeling framework to follow, each HFO/ISO VG 32 lubricating oil mixture was assumed to be a binary system, where components 1 and 2 refer to the HFO refrigerant and ISO VG 32 lubricating oil, respectively.…”

“…However, growing concerns about their high ozone depletion potential (ODP) led to the Montreal Protocol and its amendments recommending the replacement of CFCs and HCFCs by the next generation of hydrofluorocarbon (HFC) refrigerants. , Although HFCs have zero ODP, the global warning potential (GWP) for some HFCs is thousands of times greater than that of CO 2 . For example, 1,1,1,2-tetrafluoroethane (R-134a) has a GWP of 1450 (100-year time horizon) relative to CO 2 (GWP = 1). , Recently, hydrofluoroolefins (HFOs), such as 2,3,3,3-tetrafluoropropene (R-1234yf) and trans -1,3,3,3-tetrafluoropropene (R-1234ze­(E)), have been considered as two of the leading low-GWP alternatives (100-year GWP < 1) for replacing R-134a (1,1,1,2-tetrafluoroethane) in applications, such as automotive air-conditioning and foam blowing agents, respectively. − …”

“…A POE ISO VG 32 lubricating oil was selected based on its high compatibility with many refrigerants and blends and because it is a widely used POE oil for HFC and HFO compressor systems . A previous study on the vapor–liquid equilibrium ( PTx ) for R-1234yf and R-1234ze­(E) in ISO VG 32 lubricating oil has been published, where the liquid-phase HFO compositions were measured at the same temperature and pressures considered in this study . The experimental dynamic viscosity and liquid density data for each HFO/lubricating oil mixture were correlated with the well-known Redlich–Kister expansions for excess volume and “excess viscosity”.…”

“…The experimental dynamic viscosity and liquid density data for each HFO/lubricating oil mixture were correlated with the well-known Redlich–Kister expansions for excess volume and “excess viscosity”. These correlations, in addition to the previously modeled solubility data, allowed for the construction of Daniel plots, which are working diagrams that are tribologically important for compressor manufacturers.…”